1. Field of the Invention
The present invention relates to a non-volatile random access memory, and more specifically, it relates to a non-volatile random access memory (FRAM) for which ferroelectric film is employed.
2. Description of the Related Art
As typical random access memory devices, a static RAM (SRAM) and a dynamic RAM (DRAM) are well-known. Both of them are disadvantageous in that they are volatile memories, and that the former is limited in large-scale integration because it requires six transistors per a single memory cell, while the latter has to have its capacitor periodically refreshed to retain data.
In recent years, as a non-volatile random access memory device, a ferroelectric RAM (FRAM) where ferroelectric film is utilized for capacitors has become known in the art.
A circuit configuration of such a typical FRAM is shown in FIG. 5. As can be seen, the FRAM has a single memory cell essentially consisting of two transistors and two capacitor elements. In FIG. 5, there are shown MOS transistors, T1 and T2, ferroelectric film capacitor elements, C1 and C2, a drive line D, a word line W, and bit lines, B1 and B2.
In such a FRAM, setting the drive line at high voltage or ground voltage with one of the bit lines set at high voltage and the other at the ground voltage, polarization occurs in one of the capacitor elements, and thereby writing is performed in the memory. Meanwhile, applying high voltage to the drive line with both of the bit lines set at ground potential, a potential difference arises between either of the bit lines and either of the capacitor elements, and the potential difference is detected by a sense amplifier to perform reading.
Such a conventional FRAM requires two transistors and two capacitors per a single memory cell, as mentioned above, and with respect to a further increase in memory capacity and higher integration, it is desirable, to simplify the a configuration of the device.